1. Field of the Invention
The present invention relates to a vehicle vicinity monitoring apparatus for monitoring a vicinity of a vehicle with an imaging unit mounted on the vehicle.
2. Description of the Related Art
There has been developed a vehicle vicinity monitoring apparatus for obtaining images of one object with two imaging units mounted on a vehicle, either measuring the distance up to the object based on the parallax between the obtained images, or measuring the position in an actual space of the object with respect to the vehicle, and informing the driver of whether there is an obstacle ahead of the vehicle or not (see Japanese Laid-Open Patent Publication No. 2003-216937).
In order to accurately measure the position of or the distance up to the object, the angles at which the imaging units are mounted need to be determined with accuracy. Particularly, if the object exists in a distant position, then any slight difference between the mounted angles of the imaging units tends to cause a large error in the measurement of the position of or the distance up to the object. One solution is to perform an aiming process in which a target placed in a known position is imaged by the imaging units, and the mounted angles of the imaging units are determined based on the target images in the obtained images.
Templates representative of images of provisional targets may be stored in a given memory, and the position of the target in the obtained image may be determined by performing matching (template matching) on images actually obtained by the imaging units.
The aiming process is primarily carried out on vehicles in a manufacturing plant when the vehicles are shipped out of the manufacturing plant. However, the aiming process is also carried out on vehicles in various inspection facilities after the vehicles are shipped out of the manufacturing plant. Therefore, the positions of targets with respect to vehicles cannot uniformly be established, and hence it is difficult to set appropriate templates for those various inspection facilities.
Images obtained by an imaging unit may not necessarily be produced stably for various reasons, so that the positions of targets with respect to vehicles may not accurately be determined even by the template matching process.
The position of the object is determined from the images thereof in the obtained images by determining the distance up to the object based on the parallax and thereafter applying the distance to an optical perspective transformation model of the imaging unit.
The distance up to an object to be detected while the vehicle is being driven is set within a relatively long-distance range, i.e., a range from 30 m to 100 m. The distance up to the object can actually be regarded as being infinite. It is known that if the distance up to the object is infinite, a simplified perspective transformation model may be applicable for a simplified procedure for detecting the position of the object and high-speed calculations.
Generally, the aiming process is performed in indoor inspection facilities. Therefore, inspection targets are often located at a relatively short distance from the vehicle due to space limitations. With the inspection targets located at a relatively short distance from the vehicle, however, the position determined by the simplified perspective transformation model tends to suffer a large error.